I tried forcing AA from the CP but I don't think its working though I do get AA on my weapon and in some cases on some edges in the game but in most cases it doesn't work.
I'm using 158.18 drivers (8800GTS)

edit:

I installed patch v1.2 and in its readme says:

This patch allows you to turn on full-screen anti-aliasing. To turn it on you must modify the value of the following variable:

The software will automatically degrade the value of r_multisample_quality to the highest possible value that your hardware is capable of. In order to see the results of this change you will need to exit the game and return. Once set, the value of this variable will be preserved.

The default value for r_multisample_quality is 0 or No multi-sampling.

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Ea support answer
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In order to activate the full screen anti-aliasing this is what needs to be done:

Explore the Medal of Honor Pacific Assault Folder and create a shortcut on your desktop with the mohpa.exe. If you have installed this to a custom directory find this directory. For the default installation the file can be found here:

1. Double click and open My Computer.
2. Double click on Local Disc C.
3. Next open the Program Files folder.
4. Double click on the EA Games folder.
5. Open the Medal of Honor Pacific Assault(tm) folder.
6. Use the right mouse button and click and drag the mohpa.exe file to your desktop.
7. Select Create Shortcuts Here.

Next you will edit the shortcut you've created. To do this:

1. Right click on the EXE and set target as
* C:\Program Files\EA GAMES\Medal of Honor Pacific Assault(tm)\mohpa.exe" +set developer 1
2. From there launch the game from the shortcut you've just created.
3. During game press the ~ and that will bring up the console.
4. Type in the console r_multisample_quality x then hit Enter.
5. Once this is completed you will have activated the full screen antialiasing.